I know this is a long shot as most readers of this forum are in the USA and probably not familiar with Whitworth threads. I have just bought a job lot of die head chasers and one set of them is 3/4" x 19tpi, Whitworth tread form. I have searched Machinery's Handbook, and all other thread tables that I have and have found nothing near, let alone close to this thread. It looks like it may be a special of some kind. Has anyone any idea of what it might be?

Malc. :cool:

John Stevenson

01-31-2008, 10:05 AM

19 being pipe thread but other than that it look special.

.

Malc-Y

01-31-2008, 10:18 AM

19 being pipe thread but other than that it look special.

.
I had forgotten about pipe threads, 3/8" BSP parallel thread is 19tpi and is 0.656" on the o/d of the thread. I'll put the chasers in the die head and measure the diameter, thanks.

Malc. :cool:

Malc-Y

01-31-2008, 11:14 AM

I had forgotten about pipe threads, 3/8" BSP parallel thread is 19tpi and is 0.656" on the o/d of the thread. I'll put the chasers in the die head and measure the diameter, thanks.

Malc. :cool:

On second thoughts the chasers are quite clearly marked 3/4" x 19, if they were BSP threads they would be marked as such. They are made by Alfred Herbert Ltd. and their normal practice was only to mark the chasers that were not Whitworth form threads with the type of thread that it was, i.e. UNF and UNC chasers are clearly marked as such. If there is no thread form identity then they are Whitworth thread form.

Malc. :cool:

Timleech

01-31-2008, 01:16 PM

On second thoughts the chasers are quite clearly marked 3/4" x 19, if they were BSP threads they would be marked as such. They are made by Alfred Herbert Ltd. and their normal practice was only to mark the chasers that were not Whitworth form threads with the type of thread that it was, i.e. UNF and UNC chasers are clearly marked as such. If there is no thread form identity then they are Whitworth thread form.
Malc. :cool:

I'm just mildly confused. OK, I know, that's better than I normally am.
Are these *marked* whitworth or *assumed* to be such because they're unmarked?
Herbert chasers for BSP threads (which are, of course, Whitworth form anyway) are frequently marked 'GAS'.
I've got a couple of hundred different sets of chasers, the only 19tpi among them are for 3/8" BSP/Gas.
It does sound as though they're a 'special'. I have a few non-standard pitches, with the thread form unmarked so they will be, as you say, Whit form.

Tim

Malc-Y

01-31-2008, 02:28 PM

I'm just mildly confused. OK, I know, that's better than I normally am.
Are these *marked* whitworth or *assumed* to be such because they're unmarked?
Herbert chasers for BSP threads (which are, of course, Whitworth form anyway) are frequently marked 'GAS'.
I've got a couple of hundred different sets of chasers, the only 19tpi among them are for 3/8" BSP/Gas.
It does sound as though they're a 'special'. I have a few non-standard pitches, with the thread form unmarked so they will be, as you say, Whit form.

Tim
Tim, these chasers are just marked 3/4 x 19 so I am assuming that they are Whitworth form, I also checked with a 19 tpi Whit. screw pitch gauge that as far as I could see, holding it up against the light, was a perfect match. I am rapidly coming to the conclusion that they are specials. They appear to be new and have never been reground.

Malc. :cool:

Ian B

01-31-2008, 02:58 PM

"They appear to be new and have never been reground"

That's probably because nobody ever could find a tap to match the bloody things...

Ian

Timleech

01-31-2008, 04:10 PM

"They appear to be new and have never been reground"

That's probably because nobody ever could find a tap to match the bloody things...

Ian

If you think those are odd, I've got chasers for 1 3/16"
in 9, 10, 11 and 16 tpi. (all whit form). Any takers? Don't suppose I'll ever use them.